Tunable optical add/drop multiplexer

ABSTRACT

Optical signal devices, wavelength division multiplexer/demultiplexer optical devices, and methods of employing the same in which the core layer includes a grating and is comprised of a material whose refractive index is tuned so that the grating reflects a preselected wavelength of light. A single optical signal device can therefore be used to select a variety of wavelengths for segregation.

FIELD OF THE INVENTION

[0001] The present invention is generally directed to improvedintegrated wavelength division multiplexer/demultiplexer optical devicesin which light of a specific wavelength (or specific wavelengths) can beadded or dropped in an efficient manner. The device can be fabricatedfrom optical polymers having a large index of refraction variation withtemperature. A single filter element may be used over a wide wavelengthrange thereby providing for dynamic selection of wavelengths.

BACKGROUND OF THE INVENTION

[0002] Devices for adding/dropping wavelength coded signals (light of aspecific wavelength or wavelengths) are known in the art as disclosed inD. C. Johnson, K. O. Hill, F. Bilodeau, and S. Faucher, “New DesignConcept For A Narrowband Wavelength-Selective Optical Tap And Combiner,”Electron Lett., Vol. 23, pp. 668-669 (1987) and C. R. Giles and V.Mizrahi, “Low-Loss Add/Drop Multiplexers For WDM Lightwave Networks,”Proc. IOOC, pp. 66-67 (1995), incorporated herein by reference. Suchdevices employ optical fibers which are utilized predominantly intelecommunication systems in addition to local area networks, computernetworks and the like. The optical fibers are capable of carrying largeamounts of information and it is the purpose of devices of the presentinvention to extract/inject a selected amount of information from/ontothe fiber by segregating the information carried on different wavelengthchannels.

[0003] Devices of this type are comprised of a variety of componentswhich together provide the desired segregation of wavelength codedsignals. Integrated optical couplers and especially directional couplershave been developed to accomplish evanescent directional coupling asdisclosed in E. A. J. Marcatili, “Dielectric Rectangular Waveguide AndDirectional Couplers For Integrated Optics,” Bell Syst. Tech. J., p.2071 (1969), incorporated herein by reference. Optical signals arecoupled from one planar waveguide to another. The signals in the secondplanar waveguide propagate in the same direction in which the signalstravel in the first planar waveguide.

[0004] MMI (multimode interference) couplers have been developed toaccomplish coupling as disclosed in L. B. Soldano and E. C. M. Pennings,“Optical Multi-Mode Interference Devices Based On Self-Imaging:Principles And Applications,” J. Lightwave Technol., Vol. 13, pp.615-627 (1995), incorporated herein by reference. MMI couplers achieveself-imaging whereby a field profile input into a multimode waveguide isreproduced in single or multiple images at periodic intervals along thepropagation direction of the guide.

[0005] Optical circulators are optical coupling devices that have atleast three ports. Three-port circulators couple light entering port 1to port 2, light entering port 2 to port 3, and light entering port 3 toport 1.

[0006] Diffraction gratings (e.g. Bragg gratings) are used to isolate anarrow band of wavelengths as disclosed in K. O. Hill and G. Meltz,“Fiber Bragg Grating Technology Fundamentals And Overview,” J. LightwaveTechnol. Vol. 15, pp. 1263-1276 (1997) and T. Erdogan, “Fiber GrantingSpectra,” J. Lightwave Technol., Vol. 15, pp. 1277-1294 (1997),incorporated herein by reference. Such grating reflectors have made itpossible to construct a device for use in adding or dropping a lightsignal at a predetermined center wavelength to or from a fiber optictransmission system without disturbing other signals at otherwavelengths as disclosed in L. Eldada, S. Yin, C. Poga, C. Glass, R.Blomquist, and R. A. Norwood, “Integrated Multi-Channel OADM's UsingPolymer Bragg Grating MZI's,” Photonics Technol. Lett., Vol. 10, pp.1416-1418 (1998), incorporated herein by reference.

[0007] It would be desirable to be able to drop a wavelength with moreprecision than current devices within a dynamic range of wavelengths fora single optical signal device rather than employing multiple opticalsignal devices for the same purpose.

SUMMARY OF THE INVENTION

[0008] The present invention is generally to optical signal deviceshaving fine tuning means which provide for the more efficient control ofthe wavelength of light which is to be segregated from a multiplewavelength light signal.

[0009] The optical signal device of the present invention has a uniquearray of materials and also includes altering the temperature of theoptical signal device which provides for the precise selection of atargeted wavelength for dropping or adding an optical signal and whichprovides for the rapid change of wavelengths from one targetedwavelength to another.

[0010] In particular the optical signal device of the present inventioncomprises:

[0011] a) a substrate;

[0012] b) a pair of spaced apart cladding layers comprised of materialshaving at least similar refractive index values;

[0013] c) a core layer including a waveguide or a pair of opposedwaveguides positioned between the pair of cladding layers having arefractive index value greater than the refractive index value of thecladding layers such that the difference between refractive index valuesof the core layer and cladding layers enables a multiple wavelengthlight signal to pass through the device in a single mode;

[0014] d) a grating forming a filter means for causing a singlewavelength of light of said multiple wavelength light signal to besegregated therefrom; and

[0015] e) means for varying the refractive index of at least the corelayer to control the wavelength of the light which is to be segregatedfrom the multiple wavelength light signal.

[0016] In a preferred construction of the optical signal device at leastthe core layer is made of a thermosensitive material and the means forvarying the refractive index is by heating the thermosensitive material.The thermo-optic effect, being the preferred refractive index tuningeffect, is used as the illustrative effect throughout most of thisdisclosure. But generally, any refractive index tuning effect (e.g.,electro-optic effect, stress-optic effect) and any combination thereofcan be used in the present invention to vary the refractive index.

[0017] In a preferred construction of the optical signal device thereare two cladding layers positioned between the refractive index varyingmeans and the core with each of the two cladding layers having adifferent refractive index. Methods of fabricating the optical signaldevices of the present invention are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The following drawings in which like reference charactersindicate like parts are illustrative of embodiments of the invention andare not intended to limit the invention.

[0019]FIG. 1 is a schematic elevational view of one embodiment of afilter element of an optical signal device of the present invention;

[0020]FIG. 2 is a schematic elevational view of another embodiment of afilter element of an optical signal device of the present inventionemploying two cladding layers of different refractive indices between aheater and a core layer;

[0021]FIG. 3 is a graph showing the change in the wavelength of lightreflected by a filter element employed in the present invention as afunction of temperature;

[0022] FIGS. 4A-4C are schematic views of three embodiments of a singlefilter element in accordance with the present invention;

[0023] FIGS. 5A-B are schematic views of two embodiments of two-stageadd/drop filters using two heaters with or without a switch inaccordance with the present invention;

[0024] FIGS. 6A-6D are schematic views of four-stage add/drop filters ofthe present invention with one or more heaters and a variety of switchconfigurations;

[0025]FIG. 7 is a schematic view of a four stage add/drop filter inaccordance with the present invention where the unused channels arereturned to the bus;

[0026]FIG. 8 is a schematic view of a four stage add/drop filter of thepresent invention where the unused channels are combined directly withthe pass-through line using a 1×5 combiner;

[0027]FIG. 9 is a schematic view of a four stage add/drop filter inaccordance with the present invention employing out tuning of one edgeof the filter to reduce the number of switches and the complexity of thecombiner;

[0028]FIG. 10 is a schematic view of a four stage add/drop filter inaccordance with the present invention employing out tuning of both edgesof the filter to reduce the number of switches and the complexity of thecombiner;

[0029]FIG. 11 is a schematic view of another embodiment of a four stageadd/drop filter of the present invention employing out-tuning of theedges and a minimal number of switches; and

[0030]FIG. 12 is a schematic view of a four stage add/drop filter of thepresent invention where the unused channels are combined with thepass-through line using add filters.

DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention is directed to an optical signal device inwhich a means for varying the refractive index, preferably through theuse of a heater and thermosensitive polymers, is employed in the filterelement (e.g. Bragg grating) to produce a drop or add signal filter thatis fine tunable for dropping or adding a preselected wavelength of lightover a wide range of wavelengths.

[0032] In a preferred form of the invention, Mach-Zehnder interferometertype devices, 100% directional couplers, or multimode interference (MMI)couplers are employed having two coupling regions. Between the couplingregions comprising 3-dB directional couplers or 3-dB multimodeinterference couplers is a grating region comprised of a grating system(e.g. Bragg gratings). The waveguides in the grating region of MachZehnder type devices are typically spaced apart from each other so thatevanescent coupling does not occur in this region.

[0033] In another preferred form of the invention, a single waveguidebetween two optical circulators is employed. In the waveguide is agrating region comprised of a grating system.

[0034] In accordance with a preferred form of the present invention, theoptical signal device has a unique constructed grating region made ofmaterials which are thermosensitive i.e which have relatively largethermo-optic coefficients (defined as the change in refractive indexwith temperature) of, for example, at least 10⁻⁴/° C. in absolute value(e.g. thermosensitive polymers). Examples of thermosensitive polymersinclude cross-linked acrylates, polyimides and polymethylmethacrylates,as for example ethoxylated bisphenol diacrylate, tripropylene glycoldiacrylate and 1,6-hexanediol diacrylate.

[0035] When heating is the means for varying the refractive index in atleast the core layer, the grating region is provided with a heater (suchas an electrode of specified resistance) or other means of inducing achange of temperature of the polymer. Referring to FIG. 1 there is showna first construction of the grating region of the optical device of thepresent invention. The filter element 2 includes a core region 4 havingon each side thereof respective cladding layers 6A and 6B. The gratingis present in the core region 4 and preferably additionally in thecladding layers 6A and 6B. Above the cladding layer 6A is a heater 8which, as previously indicated, may be an electrode of specifiedresistance. Beneath the undercladding layer 6B there is provided asubstrate 10. The core layer is made of a thermosensitive polymer asdescribed above. The overcladding layer 6A and undercladding layer 6Bare also preferably made of similar materials although the refractiveindex of the respective layers will differ as discussed hereinafter.

[0036] In accordance with the present invention, a heater is provided inproximity to the filter element to heat the thermosensitive polymers. Asshown in FIG. 3, as the temperature of the filter element is increased,the wavelength of the reflected light will change, typically in a linearslope. As shown specifically in the example of FIG. 3, the wavelength ofthe reflected light will decrease 0.256 nm per degree centigrade withinthe range of 20 to 100° C. The wavelength of the reflected light willvary linearly by about 20 nm within this temperature range. The presentinvention therefore changes the wavelength of the reflected light of afilter element of an optical signal device by raising or lowering thetemperature of the material used to construct the filter element.

[0037] In the embodiment shown in FIG. 1, the refractive index (n) ofthe core 4 will exceed the refractive index of both the overcladdinglayer 6A and the undercladding layer 6B. It is preferred that therefractive index of the overcladding layer 6A and the undercladdinglayer 6B be the same although they may differ so long as both are lessthan the refractive index of the core layer.

[0038] In a preferred form of the invention, the undercladding layer 6Bhas a thickness of from about 10 to 20 μm while the overcladding layer6A has a thickness of from about 5 to 10 μm. The thickness of the corelayer is preferably from about 3 to 9 μm.

[0039] A preferred filter element for use in the present invention isshown in FIG. 2. This filter element provides an additional overcladdinglayer 6C between the heater 8 and the other overcladding layer 6A. Theadditional overcladding layer 6C has a refractive index lower than thatof the overcladding layer 6A and is added because the metal elementscomprising the heater 8 have a tendency to absorb light. The additionalcladding layer 6C serves to push light away from the heater andtherefore provides less loss of the optical signal, while allowing theoverall overcladding thickness (6A and 6C) to be small enough for thecore 4 to be heated efficiently by the heater 8.

[0040] In the embodiment shown in FIG. 2, the thickness of therespective layers is the same as described above in connection with theembodiment of FIG. 1. It will be noted that the combined thickness ofthe overcladding layers 6A and 6C is preferably within the range of fromabout 5 to 10 μm.

[0041] The present invention can be applied to a cascade of opticalsignal devices (e.g. Mach-Zehnder based or directional-coupler based orwaveguide-with-isolators based single channel elements of N stages) toproduce a drop filter that is tunable over a wide range (e.g. 24 to 100nm). A heating means is applied to the filter element and when theheating means is activated, the application of heat to the polymericmaterial causes a change in the reflected wavelength of the filterelement.

[0042] Table 1 shown below illustrates the number (N) of stages neededgiven a fixed temperature range and wavelength tuning range. The valueused for tunability is 0.25 nm per degree centigrade which representsthe linear relationship between reflective wavelength and temperatureshown and described in connection with the example of FIG. 3. TABLE 1Specified Bandwidth 24 nm 32 nm 40 nm 80 nm 100 nm Number of 100 GHz(0.8 nm) Channels Temp. Tuning Range 30 40 50 100 125 Range per Stagechannels channels channels channels channels  10° C.  2.5 nm 10 stages13 stages 16 stages 32 stages 40 stages  20° C.  5.0 nm  5 stages  7stages  8 stages 16 stages 20 stages  30° C.  7.5 nm  4 stages  5 stages 6 stages 11 stages 14 stages  40° C. 10.0 nm  3 stages  4 stages  4stages  8 stages 10 stages  50° C. 12.5 nm  2 stages  3 stages  4 stages 7 stages  8 stages 100° C. 25.0 nm  1 stages  2 stages  2 stages  4stages  4 stages

[0043] As shown in Table 1, for a given temperature range there is alimit on how much tuning can occur per stage. For example, for atemperature range of 10° C. for the filter element, the range of tuningfor each stage is 2.5 nm.

[0044] The filter element will contain a fixed number of channelsdepending on the channel spacing and the bandwidth of thetelecommunications system. For example, if the telecommunications systemhas a bandwidth of 24 nm then 30 channels at 0.8 nm per channel will bepresent.

[0045] As shown in Table 1, the number of stages that are required fortuning over a given temperature range for a given bandwidth can bereadily ascertained. For example, if the polymeric material and thedesired tuning speed permit a temperature range of 30° C., the channelspacing is 0.8 nm and the bandwidth is 40 nm, six stages with a tuningrange of 7.5 nm per stage will be required. If fewer stages are desired,then a higher temperature range is employed. Less stages result in lessinsertion loss (i.e. amount of light loss in decibels, in traversing thedevice) but the speed at which the device is tuned to achieve a givenwavelength will be reduced.

[0046] If a larger number of stages are employed (i.e. a lowertemperature range) for a given bandwidth, thermal transport is morerapid. However, the larger number of stages extends the length of theoptical signal device and results in higher insertion loss. It istherefore preferred to operate with a moderate number of stages with atemperature range somewhere in the middle of the 10 to 100° C. range.

[0047] The number of stages N in Table 1 also represents M in the 1×Mswitch that is required to select the output of a single stage. The 1×Mswitch can be achieved with a series of 1×2 switches (generally, 1×Pwhere P is less than M). N becomes N−1 if the two outer stages are tunedout by a slight temperature shift outside the tuning range. It is notdesirable to tune non-edge stages since it is generally desirable to usea large tuning capability to reduce the number of stages. Selectivetuning, however, also means an extra heater and extra spacing betweensegments with different heaters whereas the whole sample can be heateduniformly if out-tuning is not employed. If out-tuning is used when thenumber of stages (N) is 2, no switching is required.

[0048] In accordance with the present invention, by changing thetemperature of the polymeric material of the filter element, it ispossible to control the wavelength which drops out in each stage of theoptical signal device. Changing the temperature causes a change in therefractive index causing a wavelength change of the light that isdropped from or added to the multiwavelength light signal in accordancewith the following formula

λ=2NA

[0049] wherein

[0050] λ is the wavelength to be dropped or added;

[0051] N is the effective refractive index of the material upon heating;and

[0052] Λ is the period of the grating.

[0053] Thus, heating, which changes N and typically to a lesser degreeΛ, enables a change to the wavelength which is to be added or dropped.

[0054] The filter element employed in the present invention isapplicable to a wide variety of optical signal devices. Referring toFIGS. 4A-4C there are shown three optical signal devices employing afilter element 2 of the present invention as shown in FIG. 1 or 2. InFIG. 4A there is shown a Mach Zehnder embodiment, in FIG. 4B there isshown a 100% directional coupler embodiment, and in FIG. 4C there isshown an embodiment employing a single waveguide between two 3-portoptical circulators 18. In all three embodiments the filter elementincludes a heater 8 transversing the grating region 20 as described inconnection with FIGS. 1 and 2. In operation, a source of light ofmultiple wavelengths enters the grating region 20 through the input port22. A single wavelength of light is reflected according to thetemperature of the grating region as determined by the heater 8. Thedesired single wavelength signal is dropped from the grating regionthrough the drop port 24 while the remaining wavelengths of light passthrough the grating region and out the “pass” port 26. The wavelengthdetermined by the heater can also be added to the wavelengths exitingthe pass port by injecting it through the “add” port 28. In the FIG. 4Aembodiment, the two 3-dB directional couplers 12 can be 3-dB MMI(multimode interference) couplers. In the FIG. 4B embodiment, the 100%directional coupler 14 can be replaced by a 100% MMI coupler. In theFIG. 4C embodiment, the 3-port optical circulators 18 can be replaced by1×2 power splitters if high insertion loss and high return reflectivitycan be tolerated.

[0055] The particular wavelength of light which is dropped from or addedto the light source can be precisely selected in accordance with thepresent invention by adjusting the heater in accordance with thedependence of the reflected wavelength to temperature shown in FIG. 3.In the example shown in FIG. 3, for each ° C. that the temperature ofthe grating region is raised, the wavelength reflected will be reducedby 0.256 nm.

[0056] The remaining wavelengths of light which pass the filter elementshown in FIGS. 4A-4C may be further processed in another filter elementto enable both dropped wavelengths to enter a single switch. Thisenables either of the wavelengths to be dropped depending on the needsof the user. Such arrangements are shown in FIGS. 5A and 5B.

[0057] Referring to FIG. 5A there are employed two filter elements 2Aand 2B, each having a heater 8A and 8B, respectively. A first selectedwavelength λ₁ will be dropped from the filter element 2A and enter a 1×2switch (shown by the numeral 30). The remaining light signal absent λ₁will pass into the second filter element 2B. The temperature of theheater will be adjusted similar to what is shown in the example of FIG.3 to drop a different wavelength of light 2 which will likewise enterthe switch 30. In the embodiment shown in FIG. 5A, both wavelengths λ₁and λ₂ are desirably employed by the user and the switch 30 enables theuser to drop either λ₁ or λ₂ through a drop port 32 depending on need.Out-tuning is preferably used in the unused stage so that none of theinformation in the usable range is lost.

[0058] The embodiment shown in FIG. 5B is similar to the embodiment ofFIG. 5A but the switch is replaced by a combiner. In this embodimentout-tuning must be used so that only the desired wavelength exits thedrop port 32.

[0059] The arrangement shown in FIG. 5A does exhibit some loss of lightintensity in the switch and the arrangement shown in FIG. 5B exhibitstypically a greater loss (about 3-dB) but such loss is acceptable whenthe need is to have more than one stage in order to access a widerwavelength range and/or increase the tuning speed.

[0060] An out-tuned wavelength is a wavelength that lies outside of therange of wavelengths available within the temperature range of theheater as shown in the example of FIG. 3. For example, if a grating isof the type measured in FIG. 3 and the heater has a selected temperaturerange of from 40° C. to 80° C. the tunable wavelengths available rangefrom about 1563 nm to 1553 nm.

[0061] Say a second grating such that, for the same temperature range,it filters wavelengths ranging from 1553 nm to 1543 nm. An out-tunedwavelength therefore would fall outside of the total range (e.g. 1564 nmor 1542 nm). Thus, referring to FIG. 5B, if λ₁ is within the tunablerange and λ₂ is an out-tuned wavelength, the only wavelength which willbe dropped by the combiner will be λ₁.

[0062] Four-stage arrangements for dropping selected wavelengths byemploying heaters in accordance with the present invention are shown inFIGS. 6A-6D.

[0063] Referring to FIG. 6A there is shown an embodiment of theinvention employing 4 stages and a single heater using a 1×4 switch todrop the desired wavelength signal. In the embodiment shown in FIG. 6B,instead of a 1×4 switch as shown in FIG. 6A, a series of 1×2 switchesare employed to achieve the same result.

[0064] In the embodiment shown in FIG. 6C, two heaters are employed topermit out-tuning of the edge stages. Three ports drop a singlewavelength light signal through a 1×3 switch and a fourth port drops afourth channel which is combined with the output of the 1×3 switch toform the final drop port.

[0065] The embodiment shown in FIG. 6D employs two heaters to permit outtuning of the edge stages and 1×2 switches. The outputs of the 1×2switches are combined to form the final drop port.

[0066] The outputs of unused non-out-tuned stages contain informationfrom the usable wavelength range, said information which would bedesirable to return to the bus. Such an embodiment is shown in FIG. 7where the unused channels are collected and returned. In thisembodiment, there is provided a 1×2 switch at the output of each stageto send the signal to either the drop or the pass port. The collectionof the unused channels in FIG. 7 may use, for example, a 6-dB combiner.The reinsertion of the unused channels onto the bus may use, forexample, a 3-dB combiner.

[0067] As shown in the embodiment of FIG. 8, one way to reduce the lossin the collected channels to 7-dB would be to route all four channelsand combine them with the pass through line using a 1×5 combiner. Thisincreases the loss of the pass-through channels from 3 to 7-dB. This isstill acceptable because it equalizes all the channels that end uppassing.

[0068] Tuning out the edge stages is possible in this type ofenvironment resulting in simplification of the optical circuit. As shownin FIG. 9 one less 1×2 switch is needed and the 1×5 combiner at the passport becomes a 1×3 combiner reducing the loss from 7 to 4.7-dB, althoughan additional heater is required. As shown in FIG. 10, another 1×2switch can be eliminated if one more heater is added.

[0069] In another embodiment of the invention, a modification of theembodiment shown in FIG. 10 is provided with a 1×4 combiner instead of a1×4 switch at the drop port as shown in FIG. 11.

[0070] In another embodiment of the invention, a modification of theembodiment shown in FIG. 10 is provided with add filters instead of a1×3 combiner at the pass port as shown in FIG. 12. The add filters havegratings with the same periods as the gratings of the add/drop filtersto which they correspond and they share the same heaters with (or ingeneral are heated to the same temperature as) these add/drop filters.The add filters can have very low optical loss, circumventing the factorof N loss of 1×N combiners.

[0071] It will be understood that all of the configurations shown at thedrop ports in FIGS. 5-11 can be implemented at the add ports. It willalso be understood that all of the multi-stage configurations shown inFIGS. 5-11 employing Mach-Zehnder type devices of the kind shown in FIG.4A can also employ 100% directional couplers of the kind shown in FIG.4B or single waveguides between 3-port optical circulators of the kindshown in FIG. 4C.

What is claimed:
 1. An optical signal device comprising: a) a substrate;b) a pair of first and second spaced apart cladding layers comprised ofmaterials having at least similar refractive index values; c) a corelayer including a waveguide or a pair of opposed waveguides positionedbetween the pair of cladding layers having a refractive index valuegreater than the refractive index value of the first and second claddinglayers such that the difference between the refractive index values ofthe core layer and the cladding layers enables a multiple wavelengthlight signal to pass through the device in a single mode; d) a gratingforming a filter means for causing a single wavelength of light of saidmultiple wavelength light signal to be segregated therefrom; and e)means for varying the refractive index of at least the core layer tothereby control the wavelength of the light which is to be segregatedfrom the multiple wavelength light signal.
 2. The optical signal deviceof claim 1 wherein at least the core layer is made of a thermosensitivematerial, said means for varying the refractive index of at least thecore layer comprising a heater.
 3. The optical signal device of claim 1in the form of a Mach-Zehnder interferometer integrated with a tunablegrating.
 4. The optical signal device of claim 1 in the form of a 100%directional coupler or a 100% MMI (multimode interference) couplerintegrated with a tunable grating.
 5. The optical signal device of claim1 in the form of a single waveguide integrated with a tunable gratingbetween two 3-port optical circulators or two 1×2 power splitters. 6.The optical signal device of claim 2 wherein the thermosensitivematerial has a relatively large thermo-optic coefficient of at leastabout 10⁻⁴/C in absolute value.
 7. The optical signal device of claim 6wherein the thermosensitive material is at least one thermosensitivepolymer. 8 The optical signal device of claim 7 wherein thethermosensitive polymer is selected from the group consisting ofcross-linked acrylates, polyimides and polymethylmethacrylates.
 9. Theoptical signal device of claim 1 wherein the refractive index of thefirst and second cladding layers are the same.
 10. The optical signaldevice of claim 1 further comprising a third cladding layer positionedabove the core layer.
 11. The optical signal device of claim 10 whereinthe third cladding layer has a refractive index less than the first andsecond cladding layers.
 12. The optical signal device of claim 1 whereinthe thickness of the core layer is from about 3 to 9 um.
 13. The opticalsignal device of claim 1 wherein the second cladding layer is positionedbetween the core layer and the substrate, the second cladding layerhaving a thickness of from about 10 to 20 um.
 14. The optical signaldevice of claim 1 wherein the first cladding layer has a thickness offrom about 5 to 10 um.
 15. A wavelength divisionmultiplexer/demultiplexer optical device comprising a plurality ofintegrated optical signal devices, each of said optical signal devicescomprising: a) a substrate; b) a pair of spaced apart cladding layerscomprised of materials having at least similar refractive index values;c) a core layer including a waveguide or a pair of opposed waveguidespositioned between the pair of cladding layers having a refractive indexvalue greater than the refractive index value of the cladding layerssuch that the difference between refractive index values of the corelayer and cladding layers enables a multiple wavelength light signal topass through the device in a single mode; d) a grating forming a filtermeans for causing a single wavelength of light of said multiplewavelength light signal to be segregated therefrom; and e) means forvarying the refractive index of at least the core layer to therebycontrol the wavelength of the light which is to be segregated from themultiple wavelength light signal.
 16. The optical device of claim 15wherein at least the core layer is made of a thermosensitive material,said means for varying the refractive index of at least the core layercomprising a heater.
 17. The optical device of claim 15 where each ofthe plurality of integrated optical signal devices is in the form of aMach-Zehnder interferometer integrated with a tunable grating.
 18. Theoptical device of claim 15 where each of the plurality of integratedoptical signal devices is in the form of a 100% directional coupler or a100% MMI (multimode interference) coupler integrated with a tunablegrating.
 19. The optical device of claim 15 where each of the pluralityof integrated optical signal devices is in the form of a waveguideintegrated with a tunable grating between two 3-port optical circulatorsor two 1×2 power splitters.
 20. The optical device of claim 15 furthercomprising at least one switch for receiving at least one selectedwavelength of light from the optical signal devices and for selectivelyemploying one of said received wavelengths of light.
 21. The opticaldevice of claim 15 further comprising at least one combiner forreceiving at least one selected wavelength of light from the opticalsignal devices.
 22. The optical device of claim 15 further comprisingout-tuning means for out-tuning a wavelength of light from at least oneof said optical signal devices.
 23. The optical device of claim 22wherein the out-tuning means comprises gratings for different opticalsignal devices filtering different ranges of wavelength; at least one ofsaid gratings reflecting an out-tuned wavelength falling outside therange of usable wavelengths.
 24. The optical device of claim 15 furthercomprising means for returning at least one unused wavelength generatedwithin the range of usable wavelengths to the non-segregated wavelengthsignal passing through the optical device.
 25. The optical device ofclaim 24 further comprising add filters for returning unused wavelengthsgenerated within the range of usable wavelengths to the non-segregatedwavelength signal passing through the optical device.
 26. A method ofdropping/adding a preselected wavelength of light from/to an opticalsignal comprising passing said optical signal through an optical signaldevice comprising: a) a substrate, b) a pair of first and second spacedapart cladding layers comprised of materials having at least similarrefractive index values, c) a core layer including a waveguide or a pairof opposed waveguides positioned between the pair of cladding layershaving a refractive index value greater than the refractive index valueof the first and second cladding layers, d) a grating forming a filtermeans, e) means for varying the refractive index of at least the corelayer; and varying the refractive index to thereby reflect saidpreselected wavelength of light.
 27. The method of claim 26 where atleast the core layer is made of a thermosensitive material, and saidoptical signal device comprising a heater, said method comprisingvarying the temperature of the heater so that the thermosensitivematerial reflects a preselected wavelength of light.